The present invention relates to a method and apparatus for writing servo information onto a magnetic disk in a magnetic disk drive, and more particularly to a rewrite method that is used when the servo information is not normally written.
The magnetic disk drive has a magnetic head, which reads data recorded on a magnetic disk or writes data onto the magnetic disk. The magnetic head is mounted in an actuator mechanism, which is oscillated by a VCM (Voice Coil Motor). When the magnetic head reads or writes data, the actuator mechanism is driven to move and position the magnetic head over a designated track. Motion control is exercised in accordance with servo information, which is recorded on the magnetic disk, so that the magnetic head moves to a designated position.
A plurality of data tracks are concentrically formed on the magnetic disk. Further, identification information and servo information, which contains a burst pattern, are prerecorded in the direction of the disk diameter. The identification information indicates the track address of each data track. The identification information, which is to be read by the magnetic head, makes it possible to determine the approximate position of the magnetic head, that is, to determine what data track corresponds to the magnetic head position. The burst pattern comprises a plurality of burst pattern rows in which signal storage areas are arrayed at fixed intervals in the direction of the disk diameter. The plurality of burst pattern rows differ in signal recording area phase. The magnetic head generates a signal in accordance with a burst pattern. The signal generated in this manner makes it possible to determine the precise position of the magnetic head. More specifically, it is possible to detect the degree of deviation (positional error) of the magnetic head from a data track to which the magnetic head corresponds.
For a magnetic disk data read or magnetic disk data write operation, the magnetic head is moved until it corresponds to a specific data track while the approximate position of the magnetic head is determined in accordance with the identification information read by the magnetic head, with the magnetic disk rotating state. Then, the magnetic head is accurately positioned over a specific data track in accordance with the signal that is output from the magnetic head in accordance with a burst pattern. The data read/data write operation is performed after the magnetic head is accurately positioned as described above. The above sequence of operation is referred to as a seek operation. Further, while a data read/data write operation is being performed, feedback control is exercised in accordance with the signal that is output from the magnetic head in accordance with a burst pattern so that the magnetic head is set at a fixed position in relation to a specific data track. This operation is referred to as a track following operation.
The magnetic disk drive servo information is written from the outside by using the magnetic head of a servo track writer or written with the magnetic head of the magnetic disk drive. If the servo information cannot be written normally, it is necessary to erase the previously written information and then try again. The previously written information should be erased beforehand to avoid a situation where a plurality of sets of servo information are allowed to exist in the same track. Formerly, erasure was achieved by positioning a magnet near the magnetic disk during its rotation. However, the coercive force of the magnetic disk has increased with an increase in the degree of recording density. Therefore, the previously recorded servo information cannot be sufficiently erased.
The method disclosed by Patent Document 1 (Japanese Patent Laid-Open No. 57718/2000) is used to rewrite servo information without erasing any previously written servo information from the magnetic disk. A new servo pattern is written into a track of the disk by using a staggered wedge method. When a R/W head reaches the first track, which is positioned beyond the disk's inner crash stop (inside the inner crash stop), the first R/W head writes new servo information and then operates to write data into various sectors of the whole track. On the other hand, the other R/W heads remain inoperative. The data overwrites certain servo information existing in the track. Subsequently, the second R/W head writes new servo information and then operates to write data into various sectors of the whole track. On the other hand, the other R/W heads remain inoperative. During a power-on sequence, the R/W heads move toward a part of the disk, which is used to record the new servo pattern and new data and positioned beyond the inner crash stop, for the purpose of reading a new servo pattern.